Auxiliary torque drive for tension brake system in high speed printing press



March 17, 1970 H. E. ROSCOE ET AL AUXILIARY TORQUE DRIVE FOR TENSION BRAKE SYSTEM Filed May 27, 1968 IF'IE... 1

.IN HIGH SPEED PRINTING PRESS 3 Sheets-Sheet 1 INVENTORS HOWARD E. ROSCOE DANIEL A.WH|TE Jza ATTORNEYS March 17, 1970 sc ET AL 3,501,108

AUXILIARY TORQUE DRIVE FOR TENSION BRAKE SYSTEM IN HIGH SPEED PRINTING PRESS Filed May 27, 1968 5 Sheets-Sheet 2 BRAKES 53, 54

CONTROLS INVENTORS HOWARD E. ROSCOE DANIEL A.WHITE ATTORNEYS 3,501,108 AUXILIARY TORQUE DRIVE FOR TENSION BRAKE SYSTEM 3 Sheets-Sheet 5 H. E. RoscoE ET IN HIGH- SPEED PRINTING PRESS March 17, 1970 Filed May 27, 1968 INVENTORS HOWARD E.RO!5OOE DANIEL A. WHITE ATTORNEYS United States Patent US. Cl. 242-755 7 Claims ABSTRACT OF THE DISCLOSURE Presented is a method and means for applying a driving torque to a mill roll of material fed continuously through a printing press at speed from about 600 feet per minute to 12.00 feet per minute. To maintain a constant and uniform tension on the web being printed it is essential that the mill roll from which the web is unwound incorporate a brake system which accommodates the accelerated rotation and varying degrees of drag on the roll as the web is unwound therefrom. As the diameter of the mill roll decreases, a mill roll diameter is reached where the brake in the sense of a retarding force is no longer applied and instead of a retardation force a varying driving torque must be applied to maintain the web tension constant down to core diameter.

Background of invention The efficient operation of a continuous high speed printing process utilizing automatic or semi-automatic presses requires that the strip material to be printed, usually a web of paper or other light gauge material such as polyethylene film, be unwound from one roll called a mill roll and fed rapidly through the machine where it is acted upon at various stations and then rewound on a storage roll. Web speeds of up to 1200 feet per minute and more are not uncommon on some printing presses. When the same pattern is repeated time after time on the web as it passes through the press, the tension on the web must remain substantially constant throughout its length so that the repeat length of the pattern remains substantially constant when the web is measured in a relaxed condition. If these conditions are met, then the printed roll of web material may be mounted on another converting machine, such as a wrapper or bag machine, which is keyed in the performance of its functions to the repeat length of the pattern imprinted on the web. If the tension in the web has varied materially over its length, and the repeat patterns are not constantin their lengths, then the converting machine may not be able to cope with the variation in repeat length. It will of course be apparent that this problem is exceedingly acute when the web material is inherently resilient and is of thin gauge and low stiffness such as polyethylene film. It is therefore one of the important objects of the present invention to provide a method by which the unwind tension on a web being unwound from a mill roll may be maintained substantially constant throughout its length.

The conventional means utilized on some presses for controlling tension of the web as it unwinds from the mill roll is to use a braking system either directly con- 3,501,108 Patented Mar. 17, 1970 nected or geared to the unwinding mill roll. As the web is pulled through the press, a predetermined tensile force is applied to the web, giving consideration to the type of material, its resilience, width, gauge and stiffness characteristics. To maintain the predetermined tensile force on the web, the web frictionally engages a sensing roll of either the counterweighted dancer type or the load cell type that functions to feed a signal to the braking system to adjust the retardation torque setting of the brake in correlation to variations in web tension sensed by the sensing roll. Thus, if the sensed tension falls below the predetermined amount, the retardation torque is increased a requisite amount. If the tension increases beyond the predetermined amount, the retardation torque is decreased the requisite amount.

Various types of brake systems are conventionally used, such as electric disc brakes, electric particle brakes, pneumatic disc and shoe brakes, hydraulic pumps, torque motor systems, and DC generators. Despite the number of different types of brake systems conventionally used, the problems created by extensive variations in the width of the web material, and variations in gauge and stilfness characteristics of the web have not been solved. One of the problems is that press users are frequently custom printers for a packaging industry that requires a web which suits their own product. This requires a press sufficiently versatile to print webs having many and varied width, length, gauge and stiffness characteristics. For instance, in a given run, to obviate the necessity for splices between the webs of parent rolls, there is a tendency in the industry to use as large a diameter mill roll as possible, regardless of width, gauge, or stiffness characteristics of the web. In an attempt to meet all of the varying parameters, a brake system is usually designed of sufiicient size to accommodate the heavy gauges and wide widths of web material. To accommodate light gauges of relatively less width, change gears are provided to decrease the torque output of the brake system. Such procedure is obviously expensive an dmake-shift in nature in that there is no inherent adaptability in the brake system to accommodate the different gauges and widths of web material capable of being run through the press. Accordingly, it is another important object of the invention to provide, in conjunction with a conventional braking system, means for controlling the speed of rotation of the mill roll so that the tension of the web being fed into the press is held substantially constant.

Experience has taught that with conventional braking systems designed to accommodate heavy gauges and wide webs, when light web gauges of low stiffness and of narrow width are run at higher printing speeds, the retardation torque imposed by the brake system drops to zero before the web fully unwinds down to core diameter. This Zero torque condition is reached at varying roll diameters, depending on the gauge, width and stiffness characteristics of the web. It has been found that this zero braking torque condition is a transition point in that beyond this point in the unwinding of a roll dynamic forces that are difficult to define come into play and influence the web tension, causing the tension to increase unless remedial action is taken. These dynamic forces are a combination of windage and the continuously varying force required of the web to continuously and uniformly accelerate the rotating mass of the mill roll and core shaft system to compensate for the decrease in diameter of the mill roll.

3 It is accordingly a still further object of the invention to provide an auxiliary torque drive to the conventional web tension braking system so as to extend the range of control over the mill roll from a full diameter roll to core diameter.

Because of the high cost of large printing presses, some of which run as many as six colors at speeds up to 1000 feet per minute, it is expedient that such presses be maintained in operation for long periods or, if possible, run continuously. To run a press continuously, a web to be printed must unwind from one roll and be rewound after printing upon a second roll. By utilizing a turret apparatus in conjunction with the unwinding or feed roll, it is possible to effect a so-called flying splice between the web from an expended roll and the web of a new or full roll. This substitution of a full mill roll for an expended mill roll is effected by operating the turret to place the full mill roll in delivery position. It is one of the objects of the present invention to provide an auxiliary torque drive for a mill roll that is compatible with a turret-type flying splice apparatus.

It is a still further object of the invention to provide an auxiliary torque drive for the feed or unwind roll of a printing press, which is of simple construction and low cost and which may be applied to existing equipment.

The invention possesses other objects and features of value, some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the method and means illustrated and described, but may be embodied in various forms within the scope of the appended claims.

Summary of invention In terms of broad inclusion, the invention comprises a method and apparatus for providing auxiliary torque drive to the unwinding mill roll of a printing press for the purpose of maintaining the tension of the unwinding web of material constant. Braking systems are conventionally used in conjunction with unwind or mill feeder rolls on printing presses, but the range of control of such conventional braking systems usually does not extend to control of the web tension as the mill roll diameter approaches core diameter. When the brake torque reaches a zero condition prior to complete unwinding of the material down to the core diameter, dynamic forces become operative that cause tension in the web to increase. The method of this invention operates to add an amount of torque throughout the unwinding process that is correlated to the optimum mill roll torque to maintain web tension constant. Structurally, the additional torque may be applied to the spindle on which each mill roll is mounted, and adds torque to the spindle in appropriately varying degress from a full mill roll condition to an expended mill roll condition. To achieve such result, an electric motor supplies torque to the unwind system through a clutch. The clutch is a hysteresis or eddy current type electrical clutch with permanent magnet control. The clutch is provided with input and output sections that are relatively rotatable one with the other. When a condition of relative speed between the input and the output sections of the clutch obtains, the output section of the clutch will transmit part of the input torque applied to the input section of the clutch by the electric motor. Through appropriate belts and gears, the torque output from the clutch is applied to the mill roll. The mill roll spindle is connected through appropriate gearing to the conventional brake system, the torque output of the brake system being continuously varied by an appropriate controlling device such as a dancer roll and counterweight arranged to sense tension in the web. The electric motor and clutch of the invention add a driving torque to the mill roll which supplements the torque applied by the tension in the web in unwinding. As the roll unwinds the reduced diameter and consequent reduction in mass will require less torque Brief description of drawings FIG. 1 is a schematic illustration of a flexographic press illustrating in outline form the turret type unwinding mechanism and web tension control means. The view is shown in greatly reduced scale.

FIG. 2 is a schematic perspective view of a pair of mill rolls mounted on a turret beam, each of the mill rolls being equipped with an auxiliary torque drive in accordance with this invention.

FIG. 3 is a side elevation of the apparatus illustrated in FIG. 2, taken in the direction indicated by the arrow 3 in FIG. 2.

Description of preferred embodiment In terms of greater detail, the method and apparatus of the invention has been used successfully in conjunction with a flexographic type printing press designed for higher printing speeds of up to 1200 feet per minute and web widths of up to 60 inches. Such presses are capable of printing webs in continuous runs utilizing up to six different colors.

Briefly, uch a printing press includes a flying splice unwinding apparatus designated generally by the numeral 2, the unwinding apparatus including a turret mechanism designated generally by the numeral 3, and selectively operable to substitute a full mill roll for an expended one. As indicated in the drawing, the web 42 that is unwound from the feeder or unwind roll 39 passes through a splicing and dancer brake assembly designated generally by the numeral 7, and continues over a dancer roll 8 effective to control the infeed tension on the web.

From the in-feed tension control section, the web passes upwardly and is suspended below a main drying oven 9. From below the main oven chamber, the web passes around a draw roll 12, from whence it passes around the outer periphery of a large diameter cylinder 13 about which are suitably positioned a multiplicity of cylindrical printing plates 14, each of which is associated with a dryer hood 16 that functions to effect high velocity drying of the ink placed on the web by the cylindrical printing plates. From the cylinder 13, the web is guided through the main oven chamber, where it is subjected to heated air supplied by the main dryer burner and supply fan 17.

The printed and dried web passes out of the main dryer oven and is drawn past a web viewer 18 as shown. The viewer permits inspection of the web as it passes from the main dryer oven toward variably driven dual cooling rolls 19, from whence it passes over an out-feed pinch roll 21 and continues around a dancer roll 22 which cooperates with the web to control the rewind motor (not shown) which controls rewinding of the web on the rewind roll 23. Several different operations may be performed on the web as it passes between the dancer roll 22 and the rewind roll 23. For instance, at station 24 powder may be applied to the web to prevent offset printing of the web pattern as it is rolled on the rewind roll. If it is desired that the finished roll be less than maximum web width, a slitting station including a razor, score or shear may be positioned at 26 to effect this purpose.

It will thus be seen that because of the inherent length of the printing press, some types of which extend at least 30 feet from end-to-end, over 100 feet of web passes through the press between the unwind roll 39 and the rewind roll 23. Since the web thickness may be quite thin, in the order of 1% mills for polyethylene sheet, and since the width of the web may be as little as 24 inches, it is apparent that variations in tension on the Web will result in elongation of some sections of the web due to the inherent elasticity of the material and increased tension thereon, while other sections of the web will exhibit a contracted characteristic because of a decrease in tension thereon.

Such variations in tension and consequent variations in length have a deleterious effect on the repeat length of the pattern when the web is measured in a relaxed condition. Inasmuch as the rewind roll of printed web material is taken from the printing press illustrated and mounted on a converting machine such as a wrapper or bag machine, such converting machine may not be able to cope with the degree of variation in the repeat length caused by variations in tension on the web, and it is therefore important that control of web tension be effected throughout the full length of the web.

In conventional printing presses, the dancer rolls 8 and 22, in conjunction with appropriate control mechanisms, control the tension of the in-feed web and the outfeed web, respectively, so that the tension in the web throughout its length remains substantially constant. These dancer rolls effect their function of control by varying their positions in response to variations in web tension and thereby initiating the transmission of a signal to appropriately positioned brake systems carried in the respective turret mechanisms, which brake systems are designed to control the speed of rotation of the unwind and rewind rolls. It has been found that while control of the speed of rotation of the unwind mill roll may be effected satisfactorily when the roll is full or near full, such control is lost prior to complete unwinding of the mill roll because as soon as the brake torque setting reaches a zero condition, dynamic forces come into play to increase web tension apart from the brake system which has already reached its zero setting.

To provide the requisite control over the mill roll over the entire length of the web; e.g., to insure that adequate torque is delivered to the mill roll following the zero torque setting of the brake system and until.the core diameter of the mill roll has been reached, there is provided an auxiliary torque drive or torque helper arranged onthe turret mechanism 3 in such manner as to be carried with the turret mechanism when it substitutes a full mill roll for an expended one as is the custom with flying splice-type printing presses.

Referring specifically to FIGS. 1 and 2, the turret mechanism 3 includes a base 31 in the form of a pair of parallel spaced pedestals 32, each of which is conveniently fabricated from cast iron. The base of each pedestal is supported on a concrete floor or other supporting structure, while the upper end of each of the pedestals is provided with a suitable bearing to rotatably receive the turret shaft 33. Opposite ends of the turret shaft are appropriately supported in the bearings on pedestals so that a turret beam 34 may be supported on the shaft between the pedestals. In practice, the turret beam is preferably elongated as shown best in FIG. 2, and possesses a rectangular or square cross-section to provide rigidity and a hollow interior 36 for purposes which will hereinafter be explained.

For clarity in the description and the drawings, the pedestals have been omitted from FIG. 2. Mounted on the turret beam adjacent opposite ends thereof, are mill roll shafts or spindles 37 and 38. Each shaft is rotatably supported on the beam 34, appropriate bearings (not shown) being interposed between the shaft and the sup porting beam. The mill roll shafts 37 and 38 support mill rolls 39 and 41, respectively, mill roll 39 shown in FIGS.

2 and 3 being formed by a multiplicity of turns of the web 42, shown in FIGS. 2 and 3 as extending downwardly and threaded through the splicing rolls-dancer brake assembly 7. From this point, the web progresses as previously discussed over the in-feed tension control dancer roll 8 and thence to the cylinder 13.

To maintain tension on the web constant throughout its length, particularly as it is injected into the printing press, it is important that the mill roll that feeds the web into the press rotate at the appropriate speed commensurate with the speed of the web through the printing press, the amount of tension desired to be maintained on the web as it progresses through the press, and the decreasing diameter of the mill roll as the web unwinds, accompanied by an increasing speed of rotation of the mill roll as it unwinds. Inother Words, as the web is unwound from the mill roll, the speed of the web through the press remains constant, the speed of rotation of the mill roll will increase between a predetermined minimum with a full roll to a predetermined maximum at core diameter. This being the case, it is apparent that the torque applied to mill roll shafts 37 and 38 must vary continuously and in relation to the variations in speed of the mill roll as it unwinds.

To control the speed of rotation of the mill roll as it feeds the web into the printing press, conventional presses utilize braking systems connected directly or geared to the shafts 37 and 38. The problem arises that as the mill roll expends itself and its speed of rotation increases, the brake mechanism or system that is conventionally utilized to control the speed of rotation of the mill roll must in turn be controlled so that the tension on the web will be maintained constant.

Such brake control is initiated in conventional equipment by utilization of the dancer roll 8 which operates in conjunction with a counterweight 43, the dancer roll and counterweight both being suspended on a chain 44 running on sprockets 46 and 47 but on opposite reaches thereof. The weight of the counterweight is selected to impose the proper amount of tension on the web. Thus, referring to FIGS. 2 and 3, as tension on the web increases, the dancer roll 8 moves downwardly, with the result that the counterweight 43 moves upwardly.

Relative displacement of the dancer roll 8 and counterweight 43 results in rotation of sprocket 46, which is connected by shaft 48 and gear 49 to the driving gear 51 of a control device 52 adapted to transmit a signal to the brake mechanism shown in FIG. 2 in dash lines and designated by the numeral 53 for mill roll 39, and designated by the numeral 54 for the mill roll 41. The brake mechanisms or systems 53 and 54 may be of conventional type connected by appropriate electrical leads 56 with the control device 52. Thus, as the tension in the web increases beyond a permissible limit, the control device will transmit a signal to the brake mechanisms, backing off the braking effect and permitting the mill roll to revolve at greater speed, thus decreasing the tension on the web. Conversely, if the web tension decreases below a permissible value, the relative positions of dancer roll and counterweight will reverse and the control device will call for an increase inthe braking effect and a consequent increase in tension.

In the structure illustrated in FIGS. 2 and 3, this braking effect imposed by brake assemblies 53 and 54 is transmitted through shafts 57 and 58, respectively, to gears 59 and 61, respectively. As shown best in FIG. 2, gear 59 meshes with gear 62 keyed to shaft 37, thus imposing whatever degree of torque is appropriate on that shaft. Gear 61 on the other hand meshes with gear 63 keyed to shaft 38 on which is mounted mill roll 41. Under normal conditions, mill roll 39 is connected to the printing press and the web therefrom is drawn through the press. Mill roll 41 remains inactive until such time as mill roll 39 has been expended. Mill roll 39 is then re- 7 placed by mill roll 41 and the end of the web from mill roll 41 is spliced to the end of the web 42.

To make a flexographic press equipped with an unwind braking system as described above accommodate as many different variations in web thickness and width as is possible, and to reduce the splices between parent rolls to a minimum, there is a tendency in the industry to use as large a diameter mill roll as possible, without regard to its width, gauge and stiffness characteristics. To accommodate these variations it is customary to provide a brake system having an output torque of sufficient value to operate at optimum efficiency with heavy gauge webs of wide width. To use the same brake system for lighter gauge web materials of more narrow width, it is necessary to provide change gears to decrease the torque output of the brake system to a value correlated to the lighter gauges and narrow material.

Under these circumstances, inasmuch as the brake system is not designed to efficiently accommodate the lighter gauges and narrower widths, it sometimes happens that with light gauge webs having a low stiffness characteristic and of narrow width, particularly at higher printing speeds of the order of 600 feet per minute and higher, the brake torque drops to zero before the web unwinds all the way to the core. It has been found that when this occurs, dynamic forces will influence the web tension, causing the tension to increase. These dynamic forces are a combination force constituted by windage, and the force required of the web to accelerate the rotating mass of mill roll and core-shaft system to compensate for the increased speed of rotation of the device and increased drag that accompanies the increase in speed and decrease in diameter of the mill roll. Obviously, with the imposition of these dynamic forces and the increase in tension that results, the web will stretch and the repeat dimension of the pattern will not be uniform over the entire length of the web, thus creating problems when the rewound and printed web is placed on auxiliary converting apparatus.

To obviate this problem, there has been added to the turret assembly an auxiliary torque drive that feeds torque into the system. Referring specifically to FIGS. 2 and 3, the auxiliary torque drive for adding torque to the system includes an electric motor 66 having a drive shaft 67 terminating in a right-angle gear drive 68, the output of which is transmitted through shaft 69 to the input side of a flexible coupling or clutch 71. The output from the clutch is transmitted through an appropriate pulley 72 and V-belt 73 to pulley 74 keyed to shaft 37.

The motor 66 is conveniently an induction type electric motor cooperating with the gear drive 68 and clutch 71 to add sufficient driving torque to the core shaft 37 to supplement the torque applied by web 42, the latter value being determined by tension in the web (constant) and the radius of the mill roll (variable) as it unwinds. Thus,

the addition of the motor and clutch assembly adds only suflicient additional torque to the torque supplied by web tension to overcome the dynamic forces tending to impose a drag on the mill roll with a consequent increase in web tension.

Referring again to FIGS; 2 and 3, the shaft 38 is similarly driven by a motor 76 working through a rightangle gear drive 77 to drive the input member of a clutch 78, the output of which is connected through pulley 79 and V-belt 81, with pulley 82 keyed to shaft 38. It will of course be understood that motor 76 is not energized until such time as the turret drive is energized to substitute mill roll 41 for mill roll 39.

With respect to clutch mechanism 71, this coupling member may be of the hysteresis or eddy current type electrical clutch with permanent magnet control. One such clutch structure that has been found suitable for the application described above is a clutch mechanism utilizing twp rptors mounted so that rotation of one interacts with lines of magnetic force to rotate the other member of the clutch. The two rotors are separated by a small air gap, thus allowing magnetic lines of force to bridge the air gap and transmit power from one rotor to the other. There is no mechanical connection between the two rotors except for ball bearings which allow for free relative rotation between the rotors.

It will of course be apparent that other auxiliary torque drive type devices may be utilized in place of the magnetic clutch described above. For instance, a motor and eddy current type coupling may be used, or a motor and magnetic clutch, with appropriate controls, may be used. Additionally, under some circumstances, an electric disc clutch :would serve the purpose of adding the torque required to overcome the dynamic forces tending to impose a drag on the mill roll, or an air motor or hydraulic motor, with appropriate controls, may be substituted for the clutch described above. The system described above is preferred however because it is simple in construction and economical to manufacture and embody in existing presses.

Having thus described the invention, what is claimed to be new and desired to be protected by Letters Patent is:

1. In combination with a tension brake system for controlling the unwind tension of a web feeding into a printing press, an auxiliary torque drive for injecting torque into the system to maintain the web tension constant comprising:

(a) a motor selectively energizable to provide a moment of force;

(b) a coupling connected to said motor and including means upon which said moment of force is applied and output means for transmitting at least a portion of said moment of force; and

(0) means connecting said coupling output means to said web to apply at least a portion of said force to said web to control the tension thereof.

2. The combination according to claim 1, in which said coupling includes a pair of relatively rotatable rotors constituting input and output rotors, said input rotor is connected to said motor and said output rotor is connected to said web whereby said input and output rotors rotate at varying relative speeds to maintain the tension on said web constant.

3. The combination according to claim 1, in which said tension brake system includes a turret beat, a mill roll of said web is rotatably journaled on said beam, means mounted on said turret beam and connected to said mill roll to impose a retardation force thereon to produce a predetermined tension in the web being unwound therefrom, means associated with said means imposing said retardation force for varying the force imposed from a predetermined maximum to zero, said coupling being connected to said mill roll so as to inject a moment of force into the system before said retardation force has reached a zero value.

4. The combination according to claim 1, in which said motor provides a rotary moment of force, said web is unwound from a rotating mill roll, and said moment of force transmitted by the output means of said coupling constitutes a rotary moment applied to said mill roll to control the tension of the web being unwound therefrom.

5. The combination according to claim 1, in which said web is unwound from a mill roll rotatable at varying speeds, said coupling includes a pair of relatively rotatable rotors one of which constitutes an input rotor and the other of which constitutes an output rotor, means connected to the input rotor to drive it at a predetermined constant speed, and means connecting the output rotor to said mill roll for rotation therewith.

6. In a printing press including a mill roll from which a web is unwound and fed into the press and having a tension brake system for applying a retardation force to said mill roll in varying values between maximum and minimum limits to control the speed of rotation of said mill roll, the method of maintaining the tension on said web constant at a predetermined value, consisting of the steps of:

(a) continuously sensing the tension in said web;

(b) continuously varying said retardation force in accord with whether the value of said tension sensed is above or below said predetermined value so as to increase or decrease the speed of rotation of the mill roll; and

(c) applying to said mill roll a rotary moment of force correlated in magnitude to the magnitude of said retardation force, the speed of rotation of said mill roll and the tension in said web.

7. The method according to claim 6, in which the magnitude of said rotary moment of force is in a direction opposite to said retardation force.

References Cited UNITED STATES PATENTS NATHAN L. MINTZ, Primary Examiner 

